This project involves the development and testing of a new fluorimeter with a working volume of less than 300 nL. The fluorimeter is part of a flow through chemical analysis system. An optical fiber brings lifht from a filtered mercury light source and carries the light to the cuvette. The tip of the fiber is in the axis of the cuvette; fluorescent materials flowing past the tip are efficiently excited, and the resulting fluorescence is measured by a nearby photomultiplier. The system can detect femtomole amounts of highly fluorescent materials and picomole amounts of ammonium ions with the aid of standard enzymic assay chemistry.